Firewalls are used to help protect your computer from hackers whose main intention reside in the desire to steal information from your computer, crash your computer or delete information from your computer. The choice one makes on the type of firewall he/she wishes to adopt for his system, depends entirely on the type of operating sytem that the user has. There are basically three types of firewalls:wireless routers,hardware routers,software firewalls.
For Windows and Linux users both have a firewall is built in and is activated by default. The fact that the firewall is built into all Windows/Linux operating system does not limit the user from choosing another firewall that suits his needs once the original is turned off. One can easilty create exceptions if there is a need to recieve information from another soource eg Instant messaging, windows media player etc.
Firewalls do not protect your system fom viruses neither do they prevent you from opening e-mails that could damage your computer. In cases like these if is the user´s responsibility to install an adequate Anti-Virus program and to always update it´s signatures. Apart from this he should always exercise caution when he opens e-mails and do not know the sender.Even if one knows the sender care should be taken at all times when opening the contecnts of e-mails.
If there is not a built in firewall then there is the possibility do buy Software Firewalls to help protect your system. While this is a advantage software firewalls can only be placed on one computer and do not permit installation on various computers. In other words there can only be one software firewall for each computer and usually they are costly.
For homes that have an internet connection one generally uses hardware routers to offer protection while connected. Hardware routers offer protection to various computers and allow multiple usage.
Finally for those who use a wireless networks then there is are wireless routers that can be used. They allow one to connect laptops and generally do not use wires to connect, thus eliminating a clustered working environment. They however emit signals that can be intercepted with the right machine and generally do not come with built in firewalls, which indicates extra cost for the user.